Oscillation generator



U Y 2, 1940- w. BUSCHBECK OSCILLATION GENERATOR Filed Aug: so, 1938WERNER BUSY/ZZ- C /E BY A TTORN E Y.

Patented July 2, 1940 UNITED STATES PATENT OFFICE OSCILLATION GENERATORtion of Germany Application August 30, 1938, Serial No. 227,482 InGermany August 20, 1937 6 Claims.

The present invention is concerned with a tube circuit organizationadapted to amplify or generate alternating potentials, especially ofhigh frequency, the output of which contains only the frequency to beamplified, and is free from harmonics or overtones. It is basically wellknown in the prior art that the harmonic content of oscillations can bediminished by coupling the load to a capacitor included in the inductivebranch of the oscillatory circuit of the tube.

If this means proves insufiicient recourse may also be had to severalseries-connected tuned circuits whereby the harmonic content in terms ofpercentage may be diminished practically to any desired level. However,such circuit organizations involve the drawback that complex re-tuningis required in the different elements in case there is a change inwavelength. As a matter of fact, such re-setting is practicallyimpossible in a self-oscillatory transmitter because of the oscillationhysteresis (or pull). phenomena inhering in the multi-wave nature of thearrangement.

Now, the problem and aim of the invention is to suppress as far aspossible all harmonics in an amplifier or oscillation generator, and toprovide means for readily adjusting the apparatus to different wavelengths as desired. The invention resides in the subdivision. of thecapacity of an oscillatory circuit, in coupling the output of the tubewith one of the resultant partial capacities and the load device withthe respective other portion of the capacity, while a condenser isconnected between the junction of the said capacities and thecorresponding pointof symmetry of the inductance of the oscillationcircuit.

The invention will now be described in more detail, reference being madeto the accompanying drawing in which Figure 1 shows a circuit diagram ofan oscillation. generator which is adapted to the requirements forpracticing the invention, and

Fig. 2 shows a modified circuit arrangement.

Referring first to Fig. 1, it will be observed that the Oscillationgenerator may be either of the self-oscillatory or the master-excitedtype. The tube R has an output circuit which includes the capacitor C1of the oscillation circuit, while the load V is connected across anothercapacitor C: which is in series with the capacitor C2 merely for thepurpose of securing a voltage divison favorable to the load. The threecapacitors C1, C2 and C3 are effectively connected in series and are inparallel with the inductance of the resonant circuit. A source of directcurrent potential is supplied through the choke coil 4 to the anode ofthe tube R, is being understood that if, as shown, the cathode 3 isgrounded, then the negative terminal of said direct current source willalso be grounded.

The control grid 5 is connected through a gridleak resistor 6 and abiasing source I to the cathode 3.

The inductance of the resonant circuit comprises two portions L1 and L2,and these may be tuned jointly. The cathode 3 is directly connected tothe junction point K of the resonant circuit. Between this junctionpoint K and the junction point M for the inductances L1 and L2 isconnected a capacitor C4. For the sake of simplicity it may be assumedthat the capacitance C1 is equal to the series-capacitance C2+C3 alsothat L1=L2. If, then, a current is flowing through the oscillationcircuit it will be evident that points as regards the fundamentalfrequency of the system K and M are equi-potential points and that thecondenser C4 will play no part at all as long as its reactance is lessthan the load resistance V coupled in the lower part of the circuitbetween points K and M. This latter condition is due to the fact that inthe lower part of the circuit, as a result of series resonance of C3,C2, and L2, there remains merely the transferred active resistance ofthe load between K- and M, with capacity C4 being in parallel relationthereto. The tuning of the entire circuit'is merely a function of thequantities C1 and L1 (which, by assumption, are equal to thecorresponding elements of the lower part of the circuit) so that thetuning is effected simply in accordance with the formula which istantamount to putting XL1XC1=0, where XL and X0 are the reactances ofthe coil and of the capacity.

However, this tuning arrangement is not the only feasible one, as can beseen from the modified circuit diagram shown in Fig. 2. A state oftuning exists when the circuit between the points A and K represents anohmic resistance. Presupposing low circuit damping, this will be true asmay be confirmed by an easy calculation if XL]=XC'], as already shownabove. However, there exists a second solution, namely, when XL =Xc--l2.Xc

and this implies or corresponds to in-phase excitation of the two partsof the oscillatory circuit, the two points A and B being at the samepotential, while points K and M, on the contrary, have potentials thatare displaced an angle of 180 degrees to each other. This last-mentionedprovision for tuning will be readily understood by imagining the twopoints A and B to be inter-connected, though it is to be admitted thatthis assumption will be valid only for the fundamental wave.

The testing of a circuit organization as here disclosed showed thatthere are two possibilities for the production of oscillations, both ofwhich are equivalent and result in fundamental-wave tuning of thecircuit. In both instances the harmonic components of the output currentfrom the discharge :tube are to a large extent shortcircuited by thecapacitor C1 and the remainder of such components is substantiallydissipated after flowing through the coil L1 by virtue of a lowimpedance capacitor C4. Due to the large capacitance of the element C4,no appreciable harmonic wave potential will arise across the same. Suchremainder of harmonics as may still exist and traverse the coil L2reaches the cathode by way of the capacitors C2 and C3. the latter be--ing so large again that no appreciable potentials will be built up inthem.

In other words, capacitor C4 to a surprisingly great extent acts as ameans capable of suppressing harmonics, regardless of whether thecircuit oscillates in phase opposition (180 degrees phase difference) orwhether it oscillates in an in-phase state of tuning. The circumstancethat points K and M operate in phase opposition in the presence of inphase' excitation may be utilized in a very simple manner forself-oscillation of the circuit organization in such a way that point M,as indicated in Fig. 1 by broken lines, is united with the grid of thetube either directly or else through a condenser. The tube thus deliversto the load merely a single oscillation corresponding to in-phase tuningand practically free from harmonics. A quantitative investigation of theconditions then prevailing results in the following numerical valueswhich have been calculated by assuming a feed-back factor of k= Theleft-hand column of the tabulation contains the ordinal number of theharmonics '(n), while the other column contains the ratio between theamplitude I1 for a given harmonic, with omission of the condenser 04,and the amplitude I2 when the said condenser is included in the circuitscheme:

It will be noted therefrom that, for instance, the fourth harmonic iscut down by the factor 110 in a scheme as here disclosed as contrastedwith circuit organizations disclosed in the prior art, and this meanspractically complete suppression.

The property of point M, namely, to operate in phase opposition to theplate or anode in the presence of in-phase tuning may be utilized forthe purpose of deriving a neutralizing voltage rather than forself-oscillation of the tube. In this instance, the said point M must beun ted with the grid of the tube by way of a suitable capacity.

So far as the suppression of the harmonics is concerned it isimmaterial, as already pointed out, whether the tuning chosen for thecircuit is in phase or in phase opposition, for in either case, in caseof wave change, tuning may be obtained simply by a variation in theinductance L1, L2, the drive means of which should preferably beinter-locked mechanically. From a construction view point excitation inphase opposition of the oscillation circuit ofiers advantages in case ofmaster excitation of tube R for the reason that there is no potential offundamental wave between the points K and M so that the condenser C4 maybe made correspondingly small, and this is a very valuable fact lookedat from the angle of reduction of inner or inherent condenserinductance, for such stray inductance may play a very disturbing partwhere extremely high harmonics are dealt with. In the case ofselfoscillation of the circuit arrangement, however, in-phase tuning ispreferable, alone for the reason that the taking off of the feed-backpotential at point M becomes extremely simple. Moreover, also theharmonic potentials arising at the grid of the tube are led oil throughcondenser C4 to the cathode with the result that the other properties ofthe circuit scheme which tend to diminish the harmonics will thus beboosted.

The invention, when self-oscillatory, is particularly adapted tomeasuring and transmitter control work where the demands regardingfreedom from harmonics are very severe, while in master-excited circuitschemes the invention will be found advantageous for power stagesworking upon an open antenna.

I claim: 1. In a filter system for the output of an elec tron dischargetube, a parallel resonant circuit including a capacitor connectedbetween theanode and cathode of said tube, a second parallel resonantcircuit including a plurality of serially connected capacitors, the tworesonant circuits having equivalent and interconnected inductances,common tuning means for the two said resonant circuits, a load connectedin shunt with one only of said serially connected capacitors, and meansconnected between certain points in the capacitive and inductivebranches of said resonant circuit, said points being of substantiallyequal potential when co-phasally excited at the fundamental frequency ofsaid oscillation generae tor, for by-passing currents of higher frequen-CIBS. 2. A filter system fed with energy from a electron discharge tube,said system comprising a parallel resonant output circuit for said tube,another parallel resonant circuit having a capacitor in common with saidoutput circuit, equivalent interconnected inductances each forming apart of one of said resonant circuits respectively, common tuning meansfor the two said resonant circuits, a plurality of serially connectedcapacitors in the second said resonant circuit, and a load connectedacross one only of said capacitors, the first said capacitorconstituting means for dissipating energy of higher frequencies than thefrequency to which said resonant circuits are tuned. 3. A couplingcircuit arrangement comprising two interconnected parallel resonantcircuits, a plurality of serially connected capacitors in one of saidresonant circuits, a load in shunt with one of said capacitors, commontuning means for the two said resonant circuits, and means, in-

cluding a low impedance path for currents of harmonic frequencies withrespect to the frequency to which said resonant circuits are tuned, saidmeans being connected across selected points in the inductive andcapacitive branches of said resonant circuits and serving to dissipatesaid currents of harmonic frequencies.

4. In combination, a resonant circuit including an inductance and acapacitor, a second resonant circuit comprising an inductance and aplurality of serially connected capacitors, means common to both saidcircuits for adjusting the L/C ratio thereof in like manner and toresonate with a fundamental frequency of output from a given dischargetube, a load connected in shunt with one of the capacitors in the secondsaid resonant circuit, and means intercoupling two selected points insaid resonant circuits for dissipating harmonic frequency components ofthe output energy from said tube, one of said points being disposed onthe capacitive side of said resonant circuits, and the other of saidpoints being disposed on the inductive side of said resonant circuits.

5. The combination according to claim 4 and having means for excitingsaid selected points in phase opposition.

6. The combination according to claim 5 and having means for excitingsaid selected points co-phasally. I

WERNER BUSCI-IBECK.

